336 The Rev. D. Williams on the Killas Group of 



Fowey estuary, near Lostwithiel, and the latter not being 

 continued to either the south or the east of Dartmoor, every 

 traverse made at right angles to the direction of their strike 

 or bearing gives the same succession of the same peculiar 

 mineral deposits, and the same sections throughout the entire 

 killas region, from Torbay on the east to the Bristol channel 

 on the west. 



No. 4, though containing interpolations of red and gray grits 

 and impure calcareous beds, is usually abundantly variegated 

 as a whole, its strata being red, green, greenish gray, purple, 

 and mottled purple and green, commonly glossy and unc- 

 tuous, and of a more exquisitely delicate texture and fo- 

 liated structure than any I have ever met with. It is charac- 

 terized by the abundant remains of fish, which were first dis- 

 covered by the Messrs. Couch of Polperro, as has been fairly 

 admitted, and some of which have been exhibited to the So- 

 ciety by Mr. Peach. They preeminently characterize this 

 upper department of the killas, sometimes to such an amount 

 that I entertain no doubt that a fish-bone bed as replete with 

 their remains as that at Watchet and Aust cliff' in the 

 Lias of the Severn, will hereafter be discovered : I have my- 

 self in fact found a fragment of such Ichthyolite bed in a por- 

 tion of cliff which had fallen down on the shore, but have 

 not yet detected it in situ, — it is a consolidated congeries of 

 fish remains. Of the great number of specimens I have col- 

 lected, or which have been kindly shown me by Mr. Peach and 

 Mr. Couch, with the exception of some defensive fins and fin 

 rays which might or might not be " Onchus," they all appear 

 to me to differ even in genera from any which have hitherto 

 been figured from the Ludlow rocks or the old red sandstone. 



This member of the killas series is of considerable thick- 

 ness to the eastward, but gradually decreases in dimensions 

 as it advances to the westward : on the eastern coast it extends 

 from Man sands near Brixham, by Moss point on the Dart, 

 and East Allington and Aveton Giffbrd, to the Start and 

 Prawle points, and the Belt Head and Tail ; where, though 

 oftentimes in such conditions as refer to partial reduction by 

 active heat, and even to semifusion, it may be followed and 

 identified. Along its northern line from Man sands to near 

 the mouths of the Erme and Yealm rivers, in Bigbury bay, 

 it contains repeated interpolations of the red and gray grits 

 and red slates of the next subordinate killas series, No. 3, and 

 everywhere rests conformably upon it, with an almost perma- 

 nent southern dip as far as the parallel of Stokenham and 

 Kingsbridge, along which its beds are thrown back into a 

 fan-shaped arrangement and a high northern dip : from Slap- 



